title: Long-term effect of inoculum pretreatment on fermentative hydrogen production by repeated batch cultivations: homoacetogenesis and methanogenesis as competitors to hydrogen production.
abstract: Long-term effects of inoculum pretreatments (heat, acid, loading-shock) on hydrogen production from glucose under different temperatures (37 °C, 55 °C) and initial pH (7 and 5.5) were studied by repeated batch cultivations. Results obtained showed that it was necessary to investigate the long-term effect of inoculum pretreatment on hydrogen production since pretreatments may just temporarily inhibit the hydrogen consuming processes. After long-term cultivation, pretreated inocula did not enhance hydrogen production compared to untreated inocula under mesophilic conditions (initial pH 7 and pH 5.5) and thermophilic conditions (initial pH 7). However, pretreatment could inhibit lactate production and lead to higher hydrogen yield under thermophilic conditions at initial pH 5.5. The results further demonstrated that inoculum pretreatment could not permanently inhibit either methanogenesis or homoacetogenesis, and methanogenesis and homoacetogenesis could only be inhibited by proper control of fermentation pH and temperature. Methanogenic activity could be inhibited at pH lower than 6, both under mesophilic and thermophilic conditions, while homoacetogenic activity could only be inhibited under thermophilic condition at initial pH 5.5. Microbial community analysis showed that pretreatment did not affect the dominant bacteria. The dominant bacteria were Clostridium butyricum related organisms under mesophilic condition (initial pH 7 and 5.5), Thermoanaerobacterium sp. related organisms under thermophilic condition (initial pH 7), and Thermoanaerobacterium thermosaccharolyticum related organisms under thermophilic condition (initial pH 5.5). Results from this study clearly indicated that the long-term effects of inoculum pretreatments on hydrogen production, methanogenesis, homoacetogenesis and dominant bacteria were dependent on fermentation temperature and pH.
authors.affiliation: State Key Laboratory of Pollution Control and Resources Reuse, Tongji University, 1239 Siping Road, Shanghai 200092, PR China.
authors.forename: Gang
authors.initials: G
authors.lastname: Luo
authors.forename: Dimitar
authors.initials: D
authors.lastname: Karakashev
authors.forename: Li
authors.initials: L
authors.lastname: Xie
authors.forename: Qi
authors.initials: Q
authors.lastname: Zhou
authors.forename: Irini
authors.initials: I
authors.lastname: Angelidaki
mesh_terms: D000085:Acetates / Q000378:metabolism*; D046972:Clostridium butyricum / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects; D005285:Fermentation; D005947:Glucose / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008697:Methane / Q000378:metabolism*; D013696:Temperature; D046950:Thermoanaerobacterium / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism* / Q000528:radiation effects
chemical_list: D000085:Acetates; D006859:Hydrogen; D005947:Glucose; D008697:Methane